You also have to add in your shipping costs, and see where they divide it. It seems to work best if you wait until you need several things, and price the most expensive first, and work down to the cheapest. Then add in shipping.
I use Big Al's, Dr's F&S, & Thatfishplace for general supplies. AngelsPlus is more angel specific & has some things that are hard to find anyplace else. Brineshrimpdirect is the best place for bbs, Jehmco is another that has a big selection of fishroom supplies.